Recovery of oil from oil shale



Feb. 7, 1961 H. o. wooDRUFF 'RECOVERY oF onJ FROM on. sHALE Filed Nov. 21, 195s n r r HH; 1| \.\\\\I|V|M%Qb i l l f l l wl .l MTW! N N l u I im QU. l -QENG il @g l; K HII m .QN

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I wf United States RECOVERY F OIL FROM OIL SHALE Filed Nov. 2l, 1958, Ser. No. 775,550

Claims. (Cl. 262-3) This invention relates to a method for in situ recovery of oil from naturally occurring deposits of oil shale. The process is particularly applicable to recovery of oil and fuel gases from subterranean deposits of oil shale. In accordance with the process of this invention, oil shale is retorted in situ to liberate shale oil. The shale oil is then produced like crude petroleum. The necessary heat for the retorting operation is supplied by combustion of a portion of the shale oil within the oil shale bed.

A number of proposals have been made for the recovery of oil from underground deposits of oil shale by heating the oil shale in place, either by burning a portion of the oil or by burning an auxiliary fuel. Some of the fuel value of the shale may be recovered in the form of a heavy hydrocarbon oil or in the form of fuel gas of high calorific value, or gas rich in carbon monoxide and hydrogen suitable for use as synthesis gas or a source of hydrogen. When in situ combustion is employed for retorting, generally only a relatively small portion of the fuel value of the shale, e.g., l0 to 30 percent, is consumed as fuel in the burning operation.

In the usual proposals for retorting shale n place, passages are formed in the shale bed by explosive or hydraulic fracturing, combustion is initiated, and air or other oxygen-containing, combustion-supporting gas is forced into and through the oil shale whereby a part of the fuel value of the shale is consumed, heating the shale and releasing oil therefrom. The oil is displaced from the shale bed by the hot gases generated in the partial combustion process. A number of disadvantages stand in the way of the recovery of oil shale by these processes. A principal difficulty stems from the fact that generally the shale bed initially is highly impervious and it is di"l cult to establish uniform permeability by artificial means. It is also difficult to control the distribution and direction of ow of the gases into and through the shale bed.

In accordance with the present process, interconnected horizontal and vertical shafts are drilled through and into a shale bed, ignition is established and combustion prod? ucts collected through the vertical shaft. In a specific embodiment of this invention, one or more drifts, or passages, are formed along the lower portion of a shale bed from which oil is to be recovered. These channels may be formed either by mining or drilling, preferably by drilling, and preferably at the dip of the shale bed, to follow the course of the bed. Shale beds are often in a horizontal or near horizontal plane; consequently-horizontal or near horizontal passages may be employed in a majority of applications of the process. The process is particularly applicable to shale beds, which outcrop along a slope or cliff, such as the Mahogany Ledge formation near Rifle, Colorado. In many such cases, the edge of the shale bed is exposed and is readily reached with equipment either for horizontal drilling or mining. The process is also applicable to completely covered shale deposits; known techniques for horizontal drilling are useful in such cases.

Combustion is initiated in the passage or drift in the atefnt `ice lower part of the shale bed and the products of com# bustion and of retorting are collected and discharged through a vertical shaft or well bore. As the burning progresses in the drift along the lower portion of the shale bed, heat moves upward through the shale, releas-V ing the shale oil. The oil drains downward by gravity into the drift and is collected at the well bore, from which it may be produced through a tubing string to the surface.

The accompanying figures illustrate diagrammatically the mechanics of oil recovery from oil shale in situ retorting in accordance with the present invention.

Figs. 1 to 4 represent vertical cross sections through subterranean shale beds.

Referring to the drawings, particularly with reference to Fig. 1, shale bed 2, overlain by substantially impervious rock 3 and underlain by substantially impervious seam 4 of bed rock, is exposed along face of a clilf or slope. A horizontal passage 6 is drilled or otherwise formed in the shale bed along its lower portion, substantially parallel to its bedding plane. A substantially impervious pipe or liner 7 extends into passage 6 some distance from the face 5 of the shale bed and is cemented in place to prevent escape of gases at this point. The liner may be of steel with a refractory liner. Passage 6 is intersected by well bore 8 extending through the overburden to a point below the level of the passage. Tubing 9 extends into the well bore also to a point below passage 6. The tubing string is set in the well bore in conformity with good practice in the art of petroleum production.

In operation, air is injected through pipe 7 into the exposed end of passageway 6 at a point remote from well bore 8. A suitable fuel, eg., oil, is mixed with the air or separately introduced to form a combustible mixture. Combustion is initiated and resulting products of combustion are passed through passage 6 to the well bore 8. Gaseous combustion products are discharged through annular space S between the wall of the well bore and the tubing string to the surface of the earth. Outflow of gas and pressure in the burning and producing zone are controlled by valve 12.

During the initial period of tiring, using an auxiliary fuel, the temperature of the shale bed is raised to the retorting temperature and oil retorted from the shale bed collects in passage 6. When the rate ofoil accumulation in passage 6 is sucient to supply the fuel requirements, the introduction of auxiliary fuel may be discontinued. Combustion-supporting gas, suitably air, is continously supplied to the tiring tunnel, burning a portion of the retorted oil and further heating the shale bed. As the retorting progresses the amount of oil produced from the shale and collected in passage 6 exceeds the amount which may be burned, whereupon the excess oil flows along with the gaseous combustion products to well bore 8 where they collect in sump 8A. The oil is lifted through the tubing string 9 to the surface.

With reference to Fig. 2, the arrangement is the same as for Fig. l except that a second passage 13 in the upper portion of the shale bed is provided to carry gaseous products from the burning and retorting back through the shale bed to recover further amounts of heat from the gas and distribute this heat throughout the shale bed. By operation of valve 12, gas may be withdrawn through the well bore or forced out through passage 13. So long as the shale bed along the face of the well bore and along the upper passage 13 are relatively cold, particularly during initial phases of the operation, hydrocarbon vapors contained in the gases from the burning and retortng zone are condensed and collected in the well bore and produced through tubing 9. As the reto-rting proceeds, a point is reached when it may be desirable to process the gas externally of the formation for Patented Feb. 7, 1961.

-the recovery of condensable constituents therefrom. This may be accomplished by opening valve 12 producing gas through the annular passageway between well bore 8 and tubing 9, as in Fig..1. At this point,- passage 13 may be plugged or air may be introduced into upper passageway 13 at a point remote from the well bore, i.e. at the face of the outcrop of the shale bed, and retorting initiated in the upper passage. When air is introduced into passage 13, provided with a suitable pipe liner 14, lo-wer passage 6 may be plugged or air may be simultaneously injected through both. As an alternative, generally less desirable, gas may be produced through passage 6 and pipe 7.

Fig. 3 illustrates an alternate procedure for the production of oil from the shale stratum using the arrangement of passageways illustrated in Fig. 2. In this instance, combustion-supporting gas is first injected into the upper portion of the shale bed through passage 13. Shale in the immediate vicinity of the passage, particularly that lying above passage 13, when sufficiently heated, gives up o-il which drains into passage 13 and supports combustion thereby supplying the necessary heat for retorting the shale bed. Gaseous products of combustion pass through the shale bed along. passage 13 to the well bore 8, are conducted downward through annular passageway 10 to the lower passage 6, and then pass out to the face of the outcrop where the gases are discharged through pipe 7. Oil retorted from the shale bed in the portion of the bed between passages 13 and 6 collects in the lower passage 6 and preferably is drained into well bore 8 and produced through line 9. Alternatively, a portion of the oil may be recovered from the stream of products discharged from passageway 6. After the upper part of the shale bed is burned out, air may be introduced through pipe 7 and gas Withdrawn through the well bore by opening pipe 12 and plugging pipe 14.

Fig. 4 illustrates a further modification of my process, particularly applicable to recovery of oil from subterranean beds of oil shale which do not outcrop so that an exposed face is available. In this instance, a second well 15 is drilled through the overburden and the shale stratum as illustrated. Lower passage 6 is drilled by directional drilling from well 15 and intersected with well bore 8. Explosives Vor hydraulic fracturing may be used to establish communication between well 8 and passage 6 if the two do not .intersect when drilled. A tubing string 16 may be provided in well 15 to conduct a combustion-supporting gas to the desired level in the oil stratum. A plug or packer 17 may be provided in known manner to ensure that the combustionsupporting gas enters the stratum at the desired level. As illustrated, the oil shale is hydraulically fractured and-cement forced into the formation under pressure to prevent leakage of gas past plug 17. Valve 1S at the surface of the earth may be provided to control the flow of gas into or from the shale stratum through well 15. As illustrated in Fig. 4, apermeable section 2A is created in the upper portion of the shale stratum in suitable manner, for example, by fractnring with hydraulic pressure or explosives. Alternatively, an upper passage, similar to passage 13 of Figs. 2 and 3, may be drilled through the upper section of shale bed 2.

In a preferred method of operation as illustrated in Fig. 4, air is introduced through tubing -16 in -well 15 to lower passageway 6 where combustion is Vinitiated and carried out as previously described. The products of combustion are collected in well 8. During the initial period it is generally desirable to vent the gaseous combustion products through valve 12. As the retorting progresses and the temperature of the combustion products rises, valve 12 is closed and valve lopened, forcing the combustion products to flow from well S to well 15 through'the permeable section 2A in the upper portion .of .the oilshale'stratum. The gas is discharged from wel! 15 through valve 18. Oil retorted from the shale accumulates in well 8 and is produced through tubing 9. After the lower portion of the shale bed has been retorted and burned out, during which period some production of oil from well 15 may also take place, air may be injected into the upper portion of the shale stratum from well 15 by forcing air under pressure through valve 18, and gas again produced from well 8 through valvelZ.' As the retorting progresses, the permeability of the shale stratum greatly increases so that by the time the point is reached at which combustionsupporting gas is injected into the upper portion of the formation through. weil 15, the permeability of section 2A is high and burning and retorting proceed at a rapid rate. The retorted loil collects in Well 8 and is produced through tubing string 9.

Although I have illustrated only a single well and single passageway in Fig. l, it is to be understood that a plurality of such'k wells and passageways may be vemployed and that one or more of such passages may be connected to.y each well. With reference to Figs. 2' and 3, although ihave .shown for the purpose of illustration only an upper and v,lower horizontal passage through the shale bed, it is to be understood that a number of such vertically spaced passages may be provided, depending to a large extent upon the thickness of the shale stratum. Similarly, although only one set of well bores is illustrated, it is to be understood that multiples may be employed in .a suitable pattern, for example, the live spot o-r seven spot patterns well known in the art of secondary recovery from petroleum reservoirs by water ooding.

Obviously, many modications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should kbe made as are indicated in the appended claims.

I claim:

l. A process for obtaining shale oil froma subterranean oil shale stratum comprising forming a passage through said stratum in the lower portion thereof substantially parallel to said stratum, forming a passage along the upper portion of said stratum substantially parallel thereto, intersecting said passages with a vertical well bore, supplying combustion-supporting gas to vone of 4said passages at a point in said shale stratum remote from said well bore and `initiating combustion in said passage effecting retorting of oil from said shale, passing combustion products and retorted oil through said passage to said well bore, withdrawing retorted Aoilsubstantially free from gas through said well bore, passing gaseous products of combustion along said well bore to the other of said passages, and re-introducing said gases into and through said shale ybed through said last mentioned passage to supply'heat to said shale bed.

2. A process according to claim 1 wherein combustion is effected in saidlower passage. i

3. A process according to claim l wherein combustion is initially Vcarried out in said lower passagey effecting retorting of oil shale in the lower portion of said stratum and preheating oil shale in the upper portion of said stratum,and subsequentlythe.withdrawal ofgaseous combustion rproducts through said upper passage is discontinuedcombusti on supporting gas is then introduced into said upper passage at a point remote from said well bore, and gaseous VVproductso-f combustion discharged-separatelyl from saidoil through said well bore.

l4. A process according to claim l wherein combustionsupporting gas is initially supplied to said lower passage andgaseous products ofcombustion and retorting are dischargedthrough ysaid upper passage effecting retorting of shale in theslower portion of said stratum and preheating of r`-shale in the upper portion thereof, and subsequently the -flow of gases Vthrough said passages is reversed by introduction of combustion-supporting gas to said upper.

passage ata point'remotefromsaid well b ore anddischarge of gaseous products of combustion through said lower passage.

5. A process according to claim 1 wherein combustionsupporting gas is introduced to said lower passage through a second vertical well bore at a point remote from said first well bore.

6. A process for obtaining shale oil from a subterranean oil shale stratum comprising forming a passage through the upper portion of said stratum substantially parallel to said stratum, forming a second passage along the lower portion of said stratum substantially parallel to said upper passage, intersecting said passages with a well bore, supplying combustion-supporting gas to said upper passage at a point in said shale stratum remote from said well bore and initiating combustion in said upper passage effecting retorting of oil from the upper portion of said stratum, passing combustion products yand retorted oil through said upper passage to said Well bore, removing retorted oil substantially free from gas through said well bore, passing gaseous products of combustion along said well bore to said lower passage, passing said gaseous products of combustion through said shale stratum along said lower passage eifecting preheating of said shale in the lower portion of said stratum, and subsequently introducing combustion-supporting gas to said lower passage at a point remote from said well bore and withdrawing gaseous products of combustion separately from said oil through said well bore.

7. A process for obtaining shale oil from a subterranean oil shale stratum comprising forming a passage through said stratum in the lower portion thereof substantially parallel to said stratum, forming a passage along the upper portion of said stratum substantially parallel thereto, driving spaced well bores into said stratum, establishing communication between said passages and a plurality of said well bores, supplying combustion-supporting gas to one of said passages through one of said well bores and initiating combustion in said passage effecting retorting of oil from said shale, passing combustion products and retorted oil through said passage Ato another of said well bores, withdrawing retorted oil substantially free from gas through said last mentioned well bore, passing gaseous products of combustion through said other passage to said first well bore, and

withdrawing gaseous products of combustion and retort ing from said stratum through said first well bore.

8. A process according to claim 1 wherein said oombustion-supporting gas is supplied to said passage in the upper portion of said stratum eifecting combustion therein, and gaseous products of combustion are withdrawn through said lower passage.

9. A process for obtaining shale oil from an outcropping subterranean oil shale stratum which comprises forming a continuous open passage from its outcrop through said stratum in the lower portion thereof, interconnecting said passage with a Vertical well bore spaced from said outcrop, providing a substantially impervious liner along a portion of said passage yadjacent said outcrop, introducing combustion-supporting gas into said formation through said lined portion of said passage at said outcrop, initiating combustion in the unlined portion of said passage iat a point remote from said well bore, passing combustion products through said passage to said well bore effecting retorting of shale along the path of llow of gas through said passage and movement of retorted oil to said well bore, and withdrawing resulting retorted oil through said well bore.

10. A process according to claim 9 wherein gaseous combustion products and liquid products of retorting of said shale are separately withdrawn from said stratum through said well bore.

References Cited in the le of this patent UNTED STATES PATENTS 1,816,260 Lee July 28, 1931 2,584,605 Merriam et al. Feb. 5, 1952 2,630,306 Evans Mar. 3, 1953 2,630,307 Martin Mar. 3, 1953 2,780,449 Fisher et al. Feb. 5, 1957 2,819,761 Popham et al Ian. 14, 1958 2,874,777 Tadema Feb. 24, 1959 

